This invention relates generally to the extrusion of a plastic coating about a strand, and more specifically relates to an improved apparatus and method for extruding a thin uniform coating of plastic material about a strand, as in the production of magnet wire.
Film insulated magnet wire is conventionally manufactured by applying a solution of a synthetic resin in organic solvents to a small diameter wire and then passing the coated wire through an oven wherein the coating is baked. The application of multiple layers of resin is required to obtain a coating which meets the exacting magnet wire standards of thickness, concentricity, uniformity and surface quality.
The manufacture of magnet wire by extruding molten plastic around a wire as single layer coating has been suggested in U.S. Pat. Nos. 4,145,474, 4,165,957 and 4,379,102. The extrusion die assembly shown in the latter two patents is of a somewhat complicated and expensive construction. Because of the numerous sizes of magnet wire produced, die assemblies of this construction require a substantial investment.